Method of making diamond coated surface

ABSTRACT

THE TIPS OF ABRASIVE DIAMONDS ARE PRESSED INTO A SOFT SUBSTANCE WHILE A BONDING MATERIAL BEHIND THE DIAMONDS IS COMPRESSED AND CURED TO HOLD THEM TO A BACKING. THE   SOFT SUBSTANCE IS THEREAFTER REMOVED TO LEAVE SHARP EXPOSED ABRASIVE POINTS ON THE WORKING SIDE.

Jan. 30, 1973 J. J. BOUVIER &71

METHOD OF MAKING DIAMOND COATED SURFACE Original Filed April 26, 1967 6 Jbrz -I Bozver ATTORNEYS.

United States Patent O US. Cl. 51-295 6 Claims ABSTRACT OF THE DISCLOSURE The tips of abrasive diamonds are pressed into a soft substance while a bonding material behind the diamonds is compressed and cured to hold them to a hacking. The soft substance s thereafter removed to leave sharp exposed abrasive points on the working side.

This application is a continuation of Ser. No. 633,879, filed Apr. 26, 1967, and a continuation of Ser. No. 842,- 783 filed June 27, 1969, both abandoned.

This invention relates to diamond coated abrasives and to an improved method of making diamond coated grinding or polishing wheels, rubs, files, etc., whereby the abrasive particles (which may consist of diamonds alone or admixed with other abrasives) are applied to a hacking in a layer substantially only a single abrasive particle in depth in such a manner as to leave a sharp, free cutting face of the abrasive exposed while the abrasive granule is firmly attached to the backing material.

One objective of my invention is to make maximum use of a limited quantity of costly abrasive material.

Another objective is 'to so hold the abrasive to backing material that the cutting face of the abrasive is so exposed as to give maximum cutting ability.

Another objective is to simplify the method of manufacture of my coated articles whereby the required time is greatly reduced and certain messy Operating steps are eliminated.

In the past, abrasive articles of this sort have been made by distributing a layer of abrasive granules over an electrically conductive surface, immersing these grans in an electrolytic bath and electro plating a layer of metal such as nickel or copper onto the conductive surface down through the abrasive granules. In this way the granules immediately adjacent the conductive surface were enmeshed in the plated metal and caused to adhere to the conductive surface sutficiently tightly for the plating-coated surface to be used for abrasive purposes. Successive layers of metal were sometimes applied in this way to give firmer anchoring of the abrasive.

However there was a serious tendency of the plated layer with its included diamonds to pull away bodly from its hacking which made the article useless thereafter.

Moreover, the exposed face of the abrasive was in all cases somewhat hidden behind a certain amount of plated metal so that the maximum sharpness of the abrasive was not available for use.

I have discovered a method of manufacture whereby these various difiiculties are minim-ized or eliminated. My improved method is described below in conjunction with the accompanying drawings in which:

FIG. 1 shows a cross section through a mold loaded with my material prior to pressing and heating,

FIG. 2 shows the same cross section after pressing and heating and With my abrasive body still contained therein,

and

3-,7l3 ,795 Patented Jan. 30, 1973 FIG. 3 shows a magnied partial cross section of my finished article.

In these drawings which illustrate the formation of a simple diamond faced rnb, 1 is the barrel of a mold in WhlCh an inter-engaging steel bottom plate 2 is first placed. Next a layer 3 of relatively soft cardboard is placed next to plate 2 and above this a layer 4 of paper having an upper surface 5 of pressure sensitive adhesive. These various layers fill barrel 1 from side to side.

Next I place in the barrel and above the adhesive surface 5 a layer 6 of diamond granules just about suflicient to completely coat surface 5. These granules I gently press or roll down onto surface 5 so as to secure firm adhesion thereto, I then remove any non-adhering granules by tipping the mold and pouring them out.

I then place in the mold barrel above the abrasive granules a layer of finely divided metal powder 7 which is to serve as the material to bond my abrasive grits to a backing sheet 8 of steel which I place in the barrel above layer 7 after the powder has been leveled therein by tapping or brushing. Finally, I place an upper press plate 9 in position in the barrel.

The whole assembly is then placed in a suitable furnace and heated sufliciently to liquify at least a portion of the metal powder 7 into a softened layer 10 and to char layers 3, 4 and 5 forming a soft carbonized layer 11. While the assembly is thus heated, I place it between the platens of a hydraulic press and compress the assembly under a pressure of 50 to 200 p.s.i., thus forcing the softened metal powder into firm permanent bonding contact with both my abrasive granules and steel plate 8. This same pressure embeds the underlying points of my diamonds in layers 3, 4 and 5 which become carbonized layer 11.

When firm bonding has had time to take place between metal layer 10 and grits 6 and plate 8, I remove the mold from the press and disassemble it. The residual char is easily brushed from the face of the diamonds leaving them clean and sharp and excellent for abrasive purposes, as shown in FIG. 3 where it will be apparent that bonding metal 10 does not extend as low as to cover the exposed face of grits 6 and interfere with their abrasive action.

The foregoing description has been couched in general terms for the sake of simplicity. I shall now give examples of specific points which illustrate practices I have found to be effective although these should be regarded as examples and not as limitations.

In the first place, the rub selected for illustration is merely a representative simple form of abrasive. Various types of abrasives such as polishing pads, nail files or grinding wheels having flat working faces could obviously be made in the same way.

Secondly, while I have shown the use of pressure sensitive adhesive on a paper hacking separate from my cardboard, it would obviously be possible to have the pressure sensitive adhesive directly on the cardboard itself and except for convenience in operation, it would not be essential that the adhesive be in relatively dry for-m rather than perhaps a brushed on layer of glue or the like.

I have mentioned only diamonds as my abrasive. This is the method usually used although to reduce cost, granules of softer material, such as silicon carbide or fused alumina or even sand or granular glass can be admixed with the diamonds in any desired proportion. When used, these softer materials are generally selected to be of about the same mesh size as the diamonds.

While I have mentioned cardboard, this should be considered only as a cheap example of the general family of papers, fabrics or cloth, woven or felted, which are soft and somewhat yieldrg so the abrasive grits under pressure will become embedded in them.

As my powdered metal for bonding, I may use a variety of powders which generally will be as fine as 200 mesh and finer. I find a mixture of copper and tin (90 to tin) to be satisfactory with firing to 1900 F. during pressmg.

I select a mixture of metal powders where one has a lower melting point than the other so that when the low melting one fuses bonding is obtained. In addition to the example given, I have also used a commercially available powder mixture yielding bronze together with varying amounts of chromium boride which latter gives improved abrasion resistance and helps keep the bond in place in the final article. Bodies with these bonds I also hcat to 1900 F. prior to pressing.

EXAMPLE l To illustrate my exact procedure I shall here describe the manufacture of a diamond faced file with 3 x A inch face. To make such a file I use for my layer 6 a charge of approximately 1.5 grams of 100 mesh diamonds. After thisis distributed evenly one grain deep in my mold in contact with adhesive face 5, and my excess poured off, I place in the mold a layer 7 of 2 grams of 350 mesh metal powder as described above, then a strip of cold roller or spring steel 3 x M inches and 0.020 inch thick to form the main body of the file. A press plunger is then inserted and the assembly heated to 1900 F. and pressed as described above thus firmly afiixing the abrasive mixture to the steel strip and embedding the points of the abrasive in the charred layer 11 which is thereafter cleaned off of the face of the file.

EXAMPLE 2 As another example, I may make my layer 6 of 2 grams of a mixture of 50 parts by Volume of diamonds with 50 parts by Volume of A1 O which is gently pressed against the adhesive and any excess removed as before. Then for layer 7, I use 2 grams of 350 mesh metal powder consisting of 80% copper and 20% tin. This I process as in Example 1 except that I heat to only 1800 F. instead of to 1900 F. for bonding as in Example 1 before pressmg.

While I have described pressing in a regular press, it is also possible to heat my mold in an induction furnace or 'by resistance where the pressing can be done when the charged mold reaches the proper temperature.

In order to get proper adhesion to the metal backing plate, this should be thoroughly cleaned and preferably roughened as by sand blasting before use and I have also found it sometimes beneficial to precoat it with a suitable ux such as borax.

My abrasive bodies cut freer and last longer than similar abrasives made by earler methods. They may be recognized by the fact that the layer of abrasive grits is for the most part only a single grain in depth and the exposed or working face of each abrasive gran is clean and free from the bonding material which holds the grain to the backing material of the wheel or rub.

My abrasive articles have the further advantage that peeling of the abrasive fromthe backing is impossible and also in my articles the abrasion resistance of the bond is Very much greater than the limited resistance of the electroplated bond in the old type articles. When it is desired to have a less abrasion resistant bond, the composition may be varied or the bonding temperatures reduced by perhaps 10 F.

I have described my invention in connection with bonding with powdered metal but it can also be applied using a powdered heat setting resin bond such as the phenolic resin bonds commonly used in the abrasive industry in much the same way though the forming pressure should then be considei'ably greater, say 1000 to 2000 p.s.i. and the abrasive article should be held under pressure at curing temperature while the bond sets. The cardboard in that case can be removed later by soaking in water and 4 scrubbing with a sti& brush. The backing when using resin bonds may be any desired metal or even a strong resin impregnated stock.

The important part is to provide a single layer of abrasive grits and a soft pad into which the faces of the abrasive grits which are to be exposed for use are embedded while the bond sets and from which they will be freed before use.

I claim:

1. The method of making an abrasive faced article, comprising the steps of (a) disposng inorganic abrasive grit material onto'a yieldable, substantially unitary, coherent, penetrable, carbonizable surface layer,

(b) disposng a base metal powdered metal binder over said grit and thereby covering same,

(c) disposng a solid, substantially rigid metallic backing member over, and in intimate contact with, said powdered metal binder, said backing member having a fusion and decompostion temperature higher than both said powdered metal binder and said carbonizable layer,

(d) partial-ly depressing said grit material into said surface layer, while covered with said powdered metal binder, via pressure applied through said backing member,

(e) elevating the temperature of said binder, surface layer, grit and backing to a value below the fusion temperature of said backing member, but higher than the fusion temperature of said binder and the carbonization temperature of said surface layer,

(f) carbonizng said surface layer, fusing said metal binder and fixing said grit to said backing member via said fused binder, as a consequence of step (e),

(g) cooling the combination of step (e) below the fusion temperature of said binder,

(h) removing said carbonized layer from said grit material, to provide a shaped backing with grit material firmly bonded thereto and uniformly protruding therefrom.

2. The method of making an abrasive faced article,

comprising the steps of:

(a) disposng inorganic abrasive grit material onto a yieldable, substantially unitary, coherent, penetrable, water softenable surface layer,

(b) disposng an Organic, synthetic thermosetting resin binder over said grit and thereby covering same.

(c) disposng a solid, substantially rigid backing member over, and in intimate contact with, said resin binder,

(d) partially depressing said grit material into said surface layer, whle covered with said resin binder,

(e) e-levatng the temperature of said resin, surface layer, grit and backing to a value below both the fusion temperature of said backing member and decomposition temperature of said resin, but higher than the fusion temperature of said resin and the carbonization temperature of said surface layer,

(f) thermosetting said binder and fixing said grit to said backing member via said set binder, as a consequence of step (e),

(g) water softening said surface 'layer and removing same from said grit material, to provide a shaped backing with gritmaterial firmly bonded thereto and uniformly protruding therefrom.

3. The method of claim 1 wherein steps (d) and (e) are carried out under a pressure of from about 50-200 p.s..

4. The method of claim 1, wherein said yieldable penetrable, carbonizable surface layer has a carbonizable adhesive thereon for temporarily holding said abrasive grit material thereto during step (a).

5. The method of claim 1, wherein said yieldable penetrable, carbonizable surface layer has a carbonizable adhesive thereon for temporarily holding said abrasive g it material thereto during step (a), and. wherein steps (d) and (e) are carried out under a pressure of from about 50-200 p.s.i.

6. The method of claim 1, wherein said yeldable penetrable, carbonizable surface layer has a carbonizable adhesve thereon for temporarily holding said abrasve grit material thereto during step (a), and said surface layer is selected from the class consisting of cardboard, paper, woven and felted fabrcs.

References Cited UNITED STATES PATENTS 6 Brekke 51-297 Nash 51-297 Tone et al. 51-298.1 Crompton 51-309 Tully 51-298.1 Povech 51-298.1 Anthony 51-309 Ha'gis et al 51-309 U.S. Ol. X.R. 

